incompletely; insufficiently; partially; somewhat
Prefix that attaches to verbs or adjectives to indicate an action or state is done incompletely, insufficiently, or only partially. Not freely productive; appears in a limited set of compounds.
The 疎 in 疎か is used as a prefix expressing incompleteness.
In old texts, expressions like 疎覚え can be found, referring to insufficient memory.
The prefix 疎 (おろ) is of native Japanese origin. Its exact derivation is uncertain, but it is related to the idea of sparseness or incompleteness, as seen in words like おろそか (negligent).