Synonyms are two or more key values that hash to the same location in a master dataset. Normally, synonyms are not a problem. It just divides the right 32 bits of the key value by the dataset capacity and uses the remainder as the primary hash location. The weirdest case we have ever seen was a UK user with an R4 key field. R4 is a long floating-point, it has 64 bits, with the exponent and the most significant portion of the mantissa in the leftmost bits.
Elongation tells how inefficiently packed the chains are, relative to their optimum packing.
Just remember that every search key is there for an important on-line user need. A detail dataset with a blocking factor of 10 may have had so many puts and deletes over time that its free-entry chain points all over the place. When 10 new line items are placed on the same chain into this detail, they end up in 10 different blocks. If this detail were repacked, all 10 entries could reside in the same block. If there is more than one path, remember that a Dbunload followed by a Dbload repacks only the primary path, not all of the paths.