Genèse 35:16

And they proceeded from Beth El; and there was yet much space of provision land in the coming to Ephrath and Rahel travailed, and had hard labour in her birth.

A ‘KIVRATH’ OF LAND. Menachem ben Saruk. explained the word as having the meaning of kabir (much), i.e., great distance. A Midrashic explanation is: “At the time when the ground is full of holes like a sieve, when there was plenty of ploughed ground. The winter was past, but the dry season had not yet come.” This, however, cannot be the literal sense of the verse, for in the case of Naaman we find, And he departed from him a ‘kivrath’ of land, [which cannot possibly have this meaning since the sense there is that he had walked away but a small distance from Naaman when Gehazi immediately ran after him] . I think that it is a name for a measure of land. This is Rashi’s language.
The correct interpretation is that which Rabbi David Kimchi has advanced, i.e., that the letter kaph in the word kivrath is the kaph of comparison and is not a root letter of the word, the basic word being as in the verses: They were their ‘levaruth’ (food); ‘Vethavreini’ (and give me to eat) bread, meaning a small amount of food in the morning., and here in his commentary. And here the meaning of kivrath is the distance a pedestrian covers from morning to the time of eating, for all travellers measure distances in this manner.
This I originally wrote when still in Spain, but now that I was worthy and came to Jerusalem and Note 25 in Seder Lech Lecha. — praise to G-d Who is kind and deals kindly! — I saw with my eyes that there is not even a mile between Rachel’s grave and Bethlehem. This explanation of Rabbi David Kimchi has thus been refuted, as have the words of Menachem [ben Saruk, who said that there was a great distance between the grave and Bethlehem]. Rather kivrath is a name for a measure of land, as Rashi has said, and there is no adjectival part in the word but only a substantive as in most nouns, with the kaph serving a formative purpose to indicate that it was not an exact measure. And if the word be adjectival, modifying eretz, it is possible that brath is like bath, as in the expression, What ‘bri’ (my son)? and what “bar” (O son) of my womb? The word bath is thus the name for a small measure of land by which travellers measure the way, similar to the present day mile. It is called “bath of the land” for this small measure is as “a daughter” to the Persian mile or some other measure known in those days.
And I have also seen that …

כברת, a word which is similar to Job 34,24ירוע כבירים, “He breaks the mighty ones.” In our context it means something similar to הרבה, a considerable amount. The reason why Rachel was buried at that spot was because it was still a considerable distance from Efrat, and it would not have been dignified to transport her without a coffin for such a distance.

ותקש, this means the same as if it had said vatekashe. We have similar constructions such as ותצו as alternative for vatetzaveh, or ותכס, vatechasseh.

ויסעו...כברת, the meaning of the word כברת הארץ is equivalent to approximately 1200 meters. I believe that the letter כ here is a preposition, the name of the word describing the distance being ברת. We find a similar construction in Samuel II 12,17 ולא ברה אתם לחם “he did not even eat a little amount with them. [I do not understand the relevance of this verse to the word כברת in our verse. Ed.] The letter כ may be a כף הדמיון a letter introducing an estimate, such as כעשרים איש, about 20 men, or כאלפים אמה, approximately 2000 cubits.

ותקש בלדתה, she endured great pain during her birthing. The word ותקש may be an intransitive mode of the verb in spite of the dagesh in the letter ת, or it may be in the transitive mode meaning that the pains caused her body to become rigid, interfering with the birthing process. At any rate, she suffered extreme pain.