Ordinary boring dull boat (4)
I believe the answer is:
dory
'boat' is the definition.
(dory is a kind of boat)
'ordinary boring dull' is the wordplay.
'ordinary' becomes 'o' (abbreviation e.g. O-Levels).
'boring' indicates putting letters inside (some letters must 'bore' a hole into other letters).
'dull' becomes 'dry' (I've seen this before**).
'o' inserted into 'dry' is 'DORY'.
(Other definitions for dory that I've seen before include "another fish wanted" , "Fish of mackerel family" , "Marine fish; rhymes with fable" , "Marine fish; rowing boat" , "Fish for a small boat" .)