Interjection
A word or phrase which expresses emotion and does not form part of a sentence. English examples include Damn!, Ouch!, My Goodness!, Alas!, Hurrah!

Interrogative pronoun
A pronoun which asks a question. The English interrogative pronouns are who, what and which.
Which is your watch?
Who are you?
What do you mean?

Intransitive
The term applied to a verb which does not take an object. Some English verbs are always intransitive and can never take an object. Examples are: come, arrive, sleep, stroll, hibernate etc.

He arrived late.
Two hours elapsed.
The old man was snoring.
The baby was sleeping.

Most English verbs can be either transitive or intransitive. Note that certain intransitive verbs can be followed by noun phrases which are not objects.

Inversion
Any construction in which the ordinary word order is reversed. In subject-verb inversion, the order of the subject and an auxiliary verb is reversed.
Consider the sentence ‘John is going to the market’, in which the subject John precedes the auxiliary verb is. In the corresponding Yes-No question ‘Is John going to the market?’, the order of the subject and the auxiliary verb is inverted.

Irregular
A label applied to any linguistic item which does not behave like other items in its class typically does.

For example, the verb watch is regular, while the verb write is irregular.
I watch her.
I watched her.
I have watched her.
I write a letter.
I wrote a letter.
I have written a letter.