Wrongly deliver small part of speech among timid types (12)
I believe the answer is:
mispronounce
'wrongly deliver' is the definition.
(to pronounce or deliver in the wrong way)
'small part of speech among timid types' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'part of speech' becomes 'pronoun' (pronouns are a part of speech).
'among' is an insertion indicator.
'timid types' becomes 'mice' (mice are timid).
's'+'pronoun'='spronoun'
'spronoun' inserted into 'mice' is 'MISPRONOUNCE'.
(Another definition for mispronounce that I've seen is " Say wrongly".)