Metamorphosis contains a tense exchange of words (12)
I believe the answer is:
conversation
'exchange of words' is the definition.
'metamorphosis contains a tense' is the wordplay.
'metamorphosis' becomes 'conversion'.
'contains' means one lot of letters goes inside another.
'tense' becomes 't' (abbreviation used in many dictionaries).
'a'+'t'='at'
'conversion' going around 'at' is 'CONVERSATION'.
(Other definitions for conversation that I've seen before include "22 between people" , "discussion" , "Talk, chat" , "Spoken exchange" , "Something to talk about?" .)