The term ‘intensifier’ is used in a number of ways.
- According to one usage, the term applies to a word or phrase which modifies another word or phrase and has the function of intensifying, i.e., giving greater emotional force or emphasis to, what is modified. Examples would be ‘terribly’ in ‘He is terribly upset’, ‘extremely’ in ‘I’m extremely sorry’, ‘real‘ in ‘You’ve been a real friend to me’, and ‘utter’ in ’What he said was utter rubbish’.
Most intensifiers in this sense are either adverbs or adjectives, as in the above examples. Some are used widely, with few restrictions on the (type of) word or phrase they may modify, e.g., ‘very’, ‘really’, and ‘real’ (though for restrictions on the use of ‘very’ see Very). Others are more restricted in their use: we may say ‘She was bitterly disappointed’ or ‘It was bitterly cold’, but not ‘
He was bitterly poor'; we may say ‘He was utterly exhausted’ or ‘I am utterly amazed’, but not ‘ She is utterly ill'.
- The Oxford Dictionary of English Grammar (eds. Bas Aarts, Sylvia Chalker, and Edmund Weiner, 2nd ed., OUP 2014, s.v. intensifier) favours a different usage. Restricting the application of the term ‘intensifier’ to adverbs and adverbial phrases, it defines an intensifier as ‘an adverbial that scales another element upwards … or downwards [AWE’s emphasis]… in degrees of intensity’ (op. cit., p. 220, s.v. intensifier): it divides intensifiers into amplifiers, which raise intensity, and downtoners, which lower intensity, giving as examples of the latter ‘I hardly knew them’ and ‘We were kind of wondering’. Further, it does not understand intensity in terms of emotional force or emphasis, but equates increasing (or reducing) intensity with raising (or lowering) the degree of the modified expression (op. cit., p. 111, s.v. degree). According to this usage, there will be little, if any, difference between intensifiers and adverbs (or adverbial phrases) of degree: the adverb ‘very’, e.g., will always be an intensifier - as seems to be implied by, e.g., Collins English Dictionary (5th ed. HarperCollins Publishers, 2000, s.v., ‘very’).
- The term ‘intensifier’ is also applied, particularly in the context of etymology, to parts of words, e.g., prefixes and suffixes, when they have the function of intensifying the meaning of the principal element in the word. For example, the English verb ‘to consecrate’ comes from the Latin consecrare, in which the prefix ‘con-‘ is an intensifier, modifying the principal element in the verb, sacrare (to devote or to make sacred), so that consecrare (and hence its English derivative) means ‘to devote thoroughly or dedicate, to make completely sacred or sanctify’.
See also Emphasizer.