English
spyproof
From spy + -proof.
Formed from spy + -proof
Proto-Indo-European *speḱ- ‘to look’
…
Frankish *spehōn ‘to spy’
Vulgar Latin *spiō ‘to spy, espy’
Old French espier ‘to spy’
Middle English spien
English spy
Today it means
adj Safe from being overcome or compromised by spies.
Language periods are conventional ranges, not dates for this word.
Etymograph / spyproof