Given to bragging, several employing strange lingo (12)
I believe the answer is:
vainglorious
'given to bragging' is the definition.
(tending to be vain or boastful)
'several employing strange lingo' is the wordplay.
'several' becomes 'various' (synonyms).
'employing' means one lot of letters goes inside another.
'strange' is an anagram indicator.
'lingo' anagrammed gives 'inglo'.
'various' enclosing 'inglo' is 'VAINGLORIOUS'.
(Other definitions for vainglorious that I've seen before include "Egotistic" , "Self-important -- savouring oil (anag)" , "Boasting" , "Excessively self-proud" , "Boastful; rousing viola (anag.)" .)