List of English Words With Disputed Usage - Q

Q

• Quartary and quaternary. Quartary (from Latin: quartarius) is the fourth member of an ordinal number word series beginning with (primary, secondary, tertiary) and continuing with (quintary, sextary, ...). Quaternary (from Latin: quaternarius) is the fourth member of a distributive number word series beginning with (singular, binary, ternary) and continuing with (quinary, senary, septenary, octonary ... centenary).

In biology, the non-standard usage "quaternary structure" is so firmly entrenched that to refer to "quartary structure" would be unfamiliar.