I am learning medical terminology. My medical terminology textbook has me all confused about roots, prefixes, suffixes, and combining forms; so I have been doing some research. I've found that most dictionaries I've referenced have a different concept of a combining form versus a prefix or suffix. But even using the concept proposed by the dictionaries, I'm having trouble. Follow this link to see how Merriam-Webster distinguishes combining forms and affixes: https://www.merriam-webster.com/dictionary/combining%20form. For example, the online Merriam-Webster dictionary refers to 'hyper-' as a prefix, but "tachy-" as a combining form. I don't understand how Merriam-Webster came to that conclusion. Any insight you can provide would be greatly appreciated. Thanks.
There isn't really any clear definition of "prefix". However, in general, elements of complex words that are derived from nouns or adjectives are not called prefixes. E.g. the black in the English word blackbird is not considered to be a prefix.
Tachy- is from the the Greek adjective ταχύς.
Hyper- is from the Greek preposition/adverb ὑπέρ. It's fairly common for Greek or Latin prefixes to come from prepositions or adverbs.
"Tachy" (from ancient Greek) means "fast" as in tachycardia, tachypnea, tachygraphy, meaning fast heart rate, fast breathing and fast writing, respectively.
prefixes are defined as "morphemes (specific groups of letters with particular semantic meaning) that are added onto the beginning of roots and base words to change their meaning. Prefixes are one of the two predominant kinds of affixes—the other kind is suffixes, which come at the end of a root word."
Based on the definition of "prefix", I would say "tachy-" is a prefix and The Free Dictionary backs me up, as well as The UCL and several other sources. Whilst "tachy" is a prefix, "tachycardia" is a compound word. DC
The (vague) distinction that MW is making, as quoted by the OP, is that a "true" prefix can be affixed (with some restrictions) to a "normal" word (hence "pre-fix"), whereas a "combining form" such as "tachy-" is usually attached to another (non-word) combining form such as "-graphy".