Being sulky and low, eats seconds (9)
I believe the answer is:
moodiness
'being sulky' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'low eats seconds' is the wordplay.
'low' becomes 'moo' (both can mean to make the noise of a cow).
'eats' becomes 'dines' (dining is a kind of eating).
'seconds' becomes 's' (abbreviation).
'moo'+'dines'+'s'='MOODINESS'
'and' is the link.
Can you help me to learn more?
(Another definition for moodiness that I've seen is " State of gloom or depression".)