a substance that is undergoing an analysis of its components
"The lab technician carefully prepared the unknown sample to serve as an assay during the chemical composition study."
a written report of the results of an analysis of the composition of some substance
"The laboratory submitted its final assay detailing the exact gold content found in the ore sample."
a quantitative or qualitative test of a substance (especially an ore or a drug) to determine its components; frequently used to test for the presence or concentration of infectious agents or antibodies etc.
"The laboratory technician performed an assay on the blood sample to detect the presence of HIV antibodies."
Trial, attempt.
"After several failed attempts to fix the engine, they decided to make one final assay before giving up."
analyze (chemical substances)
"The laboratory technician will assay the water sample to detect trace levels of heavy metals."
To attempt (something).
"They decided to assay their chances of winning the championship by preparing extra hard during practice."
The word "assay" comes from the Old French essai, which originally meant a trial or test. It entered English through Middle English, where it was used as both a noun and a verb to describe trying something out.