Complement

Predicate nominative examples:

• 
  Monu is my best friend.
  (My best friend, which is a noun phrase, is functioning as the subject complement as it’s giving a new name to the subject Monu. Monu = my best friend)
  

• 
  You are a lifesaver for us.
  (Here, the noun phrase ‘a lisesaver’ is a subject complement. It is giving a new name to the subject and completing the sentence. You = a lifesaver)
  

• 
  My sister is a classical dancer.
  

(A classical dancer is a subject complement in the sentence, renaming the subject ‘my sister’.)

Multiple Meanings of "Complement"
"Complement is one of the most confusing terms in scientific grammar. Even in one grammar, we can find it being used in two ways:
a) as one of the five so-called 'clause elements', (alongside subject, verb, object and adverbial):
(20) My glass is empty. (subject complement)
(21) We find them very pleasant. (object complement)
b) as a part of a prepositional phrase, the part that follows the preposition 
(22) on the table
"In other grammars, this second meaning is extended to other phrases....It therefore appears to have very broad reference, to anything that is needed to complete the meaning of some other linguistic unit...
"These two basic meanings of complement are neatly discussed in Swan."
– Roger Berry, "Terminology in English Language Teaching: Nature and Use." Peter Lang, 2010)
"The word 'complement' is also used in a wider sense. We often need to add something to a verb, noun, or adjective to complete its meaning. If somebody says I want, we expect to hear what he or she wants; the words the need obviously don't make sense alone; after hearing I'm interested, we may need to be told what the speaker is interested in. Words and expressions which 'complete' the meaning of a verb, noun, or adjective are also called 'complements.'
"Many verbs can be followed by noun complements or -ing forms with no preposition ('direct objects'). But nouns and adjectives normally need prepositions to join them to noun or -ing form complements."
– Michael Swan, "Practical English Usage." Oxford University Press, 1995)

• 
  I want a drink, and then I want to go home.
  
• 
  Does she understand the need for secrecy?
  
• 
  I'm interested in learning to fly.
  

In many modern grammars, the object argument of a verbal predicate is called a complement. In fact, this use of the term is the one that currently dominates in linguistics. A main aspect of this understanding of complements is that the subject is usually not a complement of the predicate^]

• 
  He wiped the counter. – the counter is the object complement of the verb wiped.
  
• 
  She scoured the tub. – the tub is the object complement of the verb scoured.
  

While it is less common to do so, one sometimes extends this reasoning to subject arguments:

•