Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
kind of, a bit, rather, somewhat, sort of
These are all qualifiers suitable for various levels, and all mean essentially the same thing. We kind of [sort of] wished they’d hurry is Informal and Casual, as is I was kind of [sort of] upset by her remark. But I was somewhat [rather, a bit] upset by her remark is clearly Standard, suitable for any level, although possibly a bit stiff for some Casual use. See HAD RATHER; QUALIFIERS.
