Window or French door having first and second sashes arranged parallel to one another on either side of a closure plane and sliding in respective sliding directions (I-I) parallel to the closure plane, the first and second sashes respectively comprising a first upright and a second upright extending respectively in a first longitudinal direction (II-II) and a second longitudinal direction (III-III), said first and second uprights being intended to come into correspondence with one another to form a central upright of the window of French door when the first and second sashes are in a closure position in which they have the smallest mutual overlap, said first and second sashes being carried by rolling means allowing them to slide, said window or French door comprising: - at least one elastically compressible seal (12, 13) arranged in such a way as to be interposed between the first and second uprights when the first and second sashes are in the closure position, - a first locking member carried by the first upright and able to slide along the first upright between a locking position and a release position, - a second locking member carried by the second upright and able to slide along the second upright between a locking position and a release position, characterized in that: - the rolling means carrying the first and second sashes allow a movement of the first and second sashes in a transverse direction (V-V) perpendicular to the closure plane, - the first and second locking members are designed to bear one against the other by way of respective first and second bearing surfaces configured in such a way that: a. the movement of one of the first and second locking members towards its locking position, when the other of the first and second locking members is in the locking position, causes the first and second uprights to move towards one another in the transverse direction (V-V), b. the movement of one of the first and second locking members towards its release position, when the other of the first and second locking members is in the locking position, allows the first and second uprights to move away from one another in the transverse direction (V-V). - at least one elastically compressible seal (12, 13) arranged in such a way as to be interposed between the first and second uprights when the first and second sashes are in the closure position, - a first locking member carried by the first upright and able to slide along the first upright between a locking position and a release position, - a second locking member carried by the second upright and able to slide along the second upright between a locking position and a release position, - the rolling means carrying the first and second sashes allow a movement of the first and second sashes in a transverse direction (V-V) perpendicular to the closure plane, - the first and second locking members are designed to bear one against the other by way of respective first and second bearing surfaces configured in such a way that: a. the movement of one of the first and second locking members towards its locking position, when the other of the first and second locking members is in the locking position, causes the first and second uprights to move towards one another in the transverse direction (V-V), b. the movement of one of the first and second locking members towards its release position, when the other of the first and second locking members is in the locking position, allows the first and second uprights to move away from one another in the transverse direction (V-V). a. the movement of one of the first and second locking members towards its locking position, when the other of the first and second locking members is in the locking position, causes the first and second uprights to move towards one another in the transverse direction (V-V), b. the movement of one of the first and second locking members towards its release position, when the other of the first and second locking members is in the locking position, allows the first and second uprights to move away from one another in the transverse direction (V-V).