Just for a day, one joins that chap in the last two clues (4)
I believe the answer is:
ides
This might be a double definition.
'just for' is the first definition.
The definition suggests a singular noun which matches the answer.
'a day one joins that chap in the last two clues' is the second definition.
'ides' can be an answer for 'a day' (ides is a kind of day). I'm unsure of the rest of the definition.
Can you help me to learn more?
(Other definitions for ides that I've seen before include "ill-fated time" , "Roman calendar day roughly in the middle of the month" , "mid-month for the Romans" , "Mid-month date in Roman calendar" , "Time of March when Caesar was assassinated" .)