Final answer:
The suffixes *onym and *onomy originated from Greek, with *onym coming from the Greek word 'onyma' (name), and *onomy from 'nomos' (law or custom), used in English to form nouns describing names, terms, or systems of laws.
Step-by-step explanation:
The word-building element *onym and its variant *onomy have their origins in the Greek language. The suffix *onym, as found in words such as 'antonym,' 'synonym,' and 'pseudonym,' comes from the Greek word onyma meaning 'name.' In a similar vein, the suffix *onomy denotes a field of knowledge or laws, as seen in words like 'astronomy' or 'economy.' It derives from the Greek word nomos, meaning 'law' or 'custom.' These suffixes are found in English and are used to form nouns that describe types or systems of names, terms, or laws regarding a specific subject or field.