Record breaking old relative in leotard, say (3-5)
I believe the answer is:
one-piece
'leotard say' is the definition.
'record breaking old relative' is the wordplay.
'record' becomes 'ep'.
'breaking' means one lot of letters goes inside another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'relative' becomes 'niece' (niece is a kind of relative**).
'o'+'niece'='oniece'
'ep' put inside 'oniece' is 'ONE-PIECE'.
'in' acts as a link.
(Other definitions for one-piece that I've seen before include "(E.g. swimming costume) not as separates" , "Bathing-costume" , "Made as a single unit" , "Made as a single item" .)