Rashi on Genesis 23:9/רש"י על בראשית כ״ג:ט׳

1המכפלה MACHPELAH (the root, כפל, means double) — it had a lower and an upper cavern. Another explanation of why it was so called is, because it has the characteristic of being doubled on account of the couples who are buried there (see Rashi in verse 2) (Eruvin 53a).

2בכסף מלא FOR ITS FULL VALUE IN SILVER — מלא means שלם so that the phrase means all that it is worth. Thus, too, did David say to Ornan, (1 Chronicles 21:22) “for full money”.