Like a day in, though it's sunny out! (5)
I believe the answer is:
rainy
'sunny out' is the definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?
'like a day in though' is the wordplay.
I cannot quite see how this works, but
'like' could be 'y' (similar in meaning) and 'y' is present in the answer.
'a' is within the answer.
'in' is within the answer.
A single letter 'r' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
'it's' acts as a link.
Can you help me to learn more?
(Other definitions for rainy that I've seen before include "Pluvial" , "The day one saves for" , "Wet, showery" , "With water falling outside" , "Drizzly" .)