Eĉ se = Even if.
Example.—Ili ne volus iri, eĉ se ili estus invititaj = They would not wish to go, even if they were (should be) invited.
Foje kiam = Once when, one day when, once upon a time.
Example.—Foje kiam mi promenis, mi renkontis vian amikon = Once (one day), when walking, I met your friend.
Ĝis (also preposition) = Till, until (par. [259 (13)]).
Example.—Atendu, ĝis mi revenos[22] = Wait till I (shall) return.
Footnote:
[22] N.B.—Some writers would say ĝis kiam. Zamenhof never did—the second word appears superfluous.
Jen = Behold, here (also an adverb and interjection).
Example.—Jen la malsameco de la rezulto klariĝas = Here the difference of the result is explained.