Admittedly, there is no such thing as perfect synonymy, but the meanings of many pairs of words are close enough for this term to be used in the context of a pastime like crosswords.
( ( ( ( ( Admittedly ( , ( there ( is ( ( no ( such thing ) ) ( as ( perfect synonymy ) ) ) ) ) ) ) , ) but ) ( ( ( the meanings ) ( of ( ( many pairs ) ( of words ) ) ) ) ( are ( close ( enough ( for ( this ( term ( to ( be ( used ( in ( ( the context ) ( of ( ( a pastime ) ( like crosswords ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . )
(ROOT (S (S (ADVP (RB Admittedly)) (, ,) (NP (EX there)) (VP (VBZ is) (NP (NP (DT no) (JJ such) (NN thing)) (PP (IN as) (NP (JJ perfect) (NN synonymy)))))) (, ,) (CC but) (S (NP (NP (DT the) (NNS meanings)) (PP (IN of) (NP (NP (JJ many) (NNS pairs)) (PP (IN of) (NP (NNS words)))))) (VP (VBP are) (ADJP (RB close) (JJ enough) (PP (IN for) (NP (DT this) (NN term) (S (VP (TO to) (VP (VB be) (VP (VBN used) (PP (IN in) (NP (NP (DT the) (NN context)) (PP (IN of) (NP (NP (DT a) (NN pastime)) (PP (IN like) (NP (NNS crosswords)))))))))))))))) (. .)))
There are many words that find themselves in a relationship of perfect synonymy.
( There ( ( are ( ( many words ) ( that ( ( find themselves ) ( in ( ( a relationship ) ( of ( perfect synonymy ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (EX There)) (VP (VBP are) (NP (NP (JJ many) (NNS words)) (SBAR (WHNP (WDT that)) (S (VP (VBP find) (NP (PRP themselves)) (PP (IN in) (NP (NP (DT a) (NN relationship)) (PP (IN of) (NP (JJ perfect) (NN synonymy)))))))))) (. .)))