Old boat appearing in Omar Khayyam (3)
I believe the answer is:
ark
'old boat' is the definition.
'in omar khayyam' is the wordplay.
'in' says the answer is hidden in the clue.
'ARK' is hidden within 'omar khayyam'.
'appearing' acts as a link.
(Other definitions for ark that I've seen before include "Noah's ship" , "Noah's craft" , "Ancient shelter" , "See 18 Down" , "Rescue boat" .)