### Clue: Crucial as Poins is in effect loveless (10)
### Answer: IMPERATIVE 
 ### Explanation: Definition: Crucial
 I'M(Poins is/I am, the setter using the self-referential first person pronoun) + "operative"(in effect, as in "the new rules are operative from next month") **minus**(…less) "o"(letter signifying 0/love in tennis scores).