Most native speakers are used to “dis-” as a prefix having a negative or opposite connotation (disengaged, dissatisfied, disinterested). However, in rare cases, “dis-” is actually an amplifying prefix, most notably in “disgruntled” and “disheveled”.
Do these distinct families of “dis-” prefixed words have some common root? What’s the reason for the two nearly opposite meanings?
The relevant meaning of “dis-” in the OED is:
“With verbs having already a sense of division, solution, separation,
or undoing, the addition of dis- was naturally intensive, ‘away, out
and out, utterly, exceedingly’, as in disperīre to perish utterly,
dispudēre to be utterly ashamed, distædēre to be utterly wearied or
disgusted; hence it became an intensive in some other verbs, as
dīlaudāre to praise exceedingly, discupĕre to desire vehemently,
dissuavīrī to kiss ardently. In the same way, English has several
verbs in which dis- adds intensity to words having already a sense of
undoing, as in disalter, disaltern, disannul.”