''He was busy rummaging in his cloak''

[WilliamRota]

''He was
busy rummaging in his cloak''. What is grammaticaly both 'busy' and ''rummaging', a compound adjective?

[Grumpy]

I'll have a go. I think that "busy" is an adjective, and "rummaging" is a gerund.

[BobK]

''He was
busy rummaging in his cloak''. What is grammaticaly both 'busy' and ''rummaging', a compound adjective?

Well I wouldn't say it was adjectival; it simply says what he was doing. The word 'rummaging' explains what he was busy doing (so you're right to see the words as somehow working together).

b

[WilliamRota]

I thought if they were separated, should be used a comma left to the word ''rummaging'', right?

[BobK]

No. Rummaging is what he was busy doing.

The comma might be justified in some contexts, if the 'busyness' is more significant than the thing being done. Example: I tried to catch her attention but she was busy, looking up something on her mobile phone I think.

b

PS You mean a comma 'to the left of'; but the normal way to say it would be "a comma after the word 'busy'". You normall talk of a comma after A rather than before B. Think of the space after the comma.