ईषदर्थे

Operational rule vidhi

का is the substitute of कु when the meaning is 'a small'.

Word by word (padaccheda)

Right context ईषत्- अर्थे saptamī · ekavacana

Right context Saptamī (7th case): "when X follows", the operation applies to what precedes (1.1.66 तस्मिन्निति निर्दिष्टे पूर्वस्य). Also a condition or domain ("in the sense of").

Full reading

ईषत्-अर्थे

Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.

Commentary

का is the substitute of कु when the meaning is 'a small'.
As कामधुरम्, कालवणम्, काम्लम् ॥ Though the second member may begin with a vowel, yet this substitution takes place, in spite of 6.3.101 : as कोष्णम् ॥

Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.