a half-moon is called a semi-circle, an oval might be called a quasi-circle.
quasi adv. To some degree; almost or somewhat.
Used in combination: quasi-scientific. adj. Resembling but not being
(the thing in question). Used in combination: a quasi-victory.
In Latin quasi was employed in exactly
the same way that we would use the words "as if."
-- Updated from A Certain Je Ne Sais Quoi by
Chloe Rhodes, 2010
The two terms are not interchangeable.
"Semi" means mostly "partly."
"Quasi" means sort of "sort of."
Same with semi-nude versus quasi-nude -- to my eye, in that
case. (Come on now, one might remove half one's clothes to become
the former, but what garment does one put on to achieve the latter?)
Semi-annual makes sense.
Quasi-annual, to my ear, does not.
A woman aspiring to motherhood, I suppose, might be described
as quasi-pregnant, but not by me. As semi-pregnant, by no one.
For "quasi-scientific," isn't "unscientific" more to the
point? Try these...
We are all quasi-economists.
a quasi-executive works in the mailroom;
a quasi-doctor wears feathers and body paint;
a quasi-lawyer is his own client.
Some writers and speakers write and speak "quasi" when,
often as not, "semi" is what they really mean. I have decided not
to do that.
Maybe what they really are are quasi-writers and quasi-speakers.
Maybe that's what I am.