Forming nouns from verbs.
[Anglo-Norman French -é or -ee, from Latin -atus (past participial ending).]
Words in -ee mark the passive recipient of an action, or a person affected in some way by the action of the verbs from which they have been formed: abductee, amputee, detainee, employee, inductee, internee, interviewee, licensee, nominee, patentee, trainee. In many cases, the active agent is marked by -er (see -er1) or -or (see -or1), as in interviewer or abductor; such pairs are common in legal usage, in which the -or form is common: lessor/lessee, vendor/vendee. A committee was originally a person to whom some duty has been committed; it can still have the legal sense of a person entrusted with the charge of someone else's property.
Some examples seem active rather than passive, and have been criticized for that reason: an absentee has actively absented him- or herself; an escapee has escaped, say from prison; a returnee has returned, perhaps from active military service oversees. However, several of these, especially escapee and returnee, have a useful nuance of an action completed rather than in process.
The suffix is active in the language, often being used to create words for a single use: apologee, embalmee, introducee, phonee, suggestee, vaccinee.
Other nouns ending in -ee come from a variety of languages. Some are from Hindi words ending in -i: dungaree, puttee, puggaree. Words such as debauchee, fricassee, grandee, jubilee, marquee, squeegee, and trochee derive from French, Spanish, and other languages. The origins of bungee, filigree, jamboree, and settee are uncertain. For some examples of affectionate or diminutive terms in -ee, see -y2.