Is 'opportunistic' an adjective or a noun?

That he deployed it only on his last full day in office struck some observers as ***opportunistic***.

Question

Is 'opportunistic' an adjective or a noun?

That he deployed it only on his last full day in office struck some observers as ***opportunistic***.

Answer

... as opportunistic [behavior]

Adjective - opportunistic 
Adverb - opportunistically 
Noun - opportunist

Answer

It's an adjective. It's modifying the unmentioned or suggested "timing" or "moment" that he chose to do the deployment.

If you reword the sentence it might be clearer:
- Some observers thought that he chose an opportunistic moment to deploy it; his last day in the office.

- He chose an opportunistic time to do it.

Answer

It's usually used as an adjective, but could be used as an adverb (used to describe an action).

No pierdas la oportunidad de aprender un idioma desde la comodidad de tu casa. ¡Explora nuestra selección de profesores de idiomas con experiencia e inscríbete ya en tu primera clase!