rare
uncommon
rare as rocking horse shit
non-English
Alwin
geason
superrare
rare as a four-leaf clover
ultrarare
semirare
rareish
Isom
seldomly
unique
supersubtle
slip of the tongue
rarer than hens' teeth
inexpressable
Englishy
rare as hen's teeth
unoften
vaguity
nonvernacular
Duke
unlikelily
unvernacular
once in a blue moon
different
noneven
non-Englishness
un-English
ultrararefied
one in a million
nondialectical
adialectal
undialectical
caselessness
few and far between
seldomness
rocking horse shit
nondialectal
strictly
Hebrew
unclearly
Amata
unknown
scarce
none
unperiphrastic
although