Words ending in a double letter preserve it double after a prefix or
before a termination beginning with a different letter; as, _op-press_,
_mis-spell_, _in-thrall_, _oversee_; _see-ing_, _op-pressive_,
_stiff-ness_, _woo-ed_, _still-ness_, _assess-ment_.
_Remark I._—_Annul_, _until_, _twibil_, and the conservative
_fulfil_, or the Websterian _fulfill_, are the only exceptions
to the first part of this rule extensively recognized by
present usage. The conservative _distil_ and _instil_ are at
variance; but the Websterian _distill_ and _instill_, and also
_twibill_, as written by Reid, are in harmony with the rule.
_Remark II._—_Pontific_, and all other derivatives of pontiff,
are exceptions to the latter part of this rule, unless an _f_
is discarded in the primitive word, as Webster suggests and the
derivation warrants. The derivatives of dull, full, skill, and
will, are disputed exceptions: if spelled as Webster writes
them, _dullness_, _fullness_, _skillful_, _willful_, they
conform to the rule.