This is an item from Anton Moker's Decalogus metricus et paraenetica disticha, published in 1573. You can see the book at GoogleBooks.
Fidus Amicus
Rebus in ambiguis ex multis millibus unus
Vix constans et vix fidus amicus erit.
The vocabulary is keyed to the DCC Latin Vocabulary list. There are two words in this poem that are not on the DCC list:
ambiguus, -a, -um: uncertain, doubtful, ambiguous
fīdus, -a, -um: faithful, loyal
amīcus -a -um: friendly; (as subst.) friend
cōnstō -stāre -stitī: agree; constat, it is established that (+ infin.)
et: and
ex ē: out of, from (+ abl.)
in: in, on (+ abl.); into, onto (+ acc)
mille (pl.) milia: thousand
multus -a -um: much, many; multō, by far
rēs reī f.: thing (rēs pūblica, commonwealth; rēs familiāris, family property, estate; rēs mīlitāris, art of war; rēs novae, revolution)
sum, esse, fuī: be, exist
ūnus -a -um: one
vix: scarcely