What part of speech is "left" in the following sentence?
There was nothing left.
LEFT is the past participle form of the verb 'to leave' in the sense "remaining"
• Ther are only three cups of juice left.
••There was nothing left.
--In the above example "left" is past participle (verb-adjective) with a passive meaning; it means everything was exhausted.
Participles are verbs used as adjectives. Participles used as adjectives often come after the nouns they modify if joined by linking/copular verbs like 'be, become, seem, etc. When the past participle is used, the noun it describes is acted upon.
•I seem confused. ••The students are bored •••There was nothing left.
So "left" is a particpal adjective originated from verb 'to leave' used predicatively to mean 'remaining'.
To be precise, it is a postpositive use of adjective after the pronoun, 'Nothing'.
What is left? (There was nothing left.)
Two plausible options exist:
It's an adjective.
The sentence can be regarded as an elision of "There is nothing that is left." -- in which left is the predicate adjective in a noun phrase.
There was nothing taken.
we have an existential construction with a passive: Nothing was taken. Here, 'taken' is a past participle.
There was nothing left [on the bus by the children].
is a similar construction.
There was nothing left. [It had all gone.]
'be left' is probably best regarded as a multi-word verb (when it means 'remain', as in this case). Then, if 'left' needs a name, it is a particle.
'Be left over' is analysed as a 'phrasal verb with [simplex verb] leave' by, for instance, CDO.